Understanding the properties of materials is important in many applications. Spectroscopic techniques can be used to obtain important information about materials, particularly at or near the material surface.
One spectroscopy technique is Raman spectroscopy, based on the Raman effect. The Raman effect occurs as a result of molecular deformations in electric field E, determined by molecular polarisability a. A laser beam can be considered an oscillating electromagnetic wave with electrical vector E. Upon interaction with the sample, it induces an electric dipole moment P=a*E, which deforms molecules. Periodically deformed molecules begin vibrating with characteristic frequency νm. The amplitude of vibration is known as nuclear displacement. In other words, monochromatic laser light with frequency ν0 excites molecules and transforms them into oscillating dipoles.
Another spectroscopy technique is photoluminescence (sometimes referred to herein as “PL”). Photoluminescence is the optical emission obtained by photon excitation, typically using a laser. The energy from photons of the excitation light source excite electrons of the material from lower energy states to higher energy states. The electrons subsequently return to the lower energy state, each emitting a photon with a frequency proportional to the difference in energy between the high energy and low energy states. Photoluminescence techniques can be used for non-destructive characterization of materials, such as semiconductors. One common use of photoluminescence spectroscopy is to determine material composition, since different materials emit photons of different wavelengths, depending on the particular transition generating the photon.